Nashville was never big enough to contain Taylor Swift. So for her fourth album, she turned to Sweden for a pop-hit crash course from the biggest expert she should find: Max Martin. After spending her teens dominating the pop charts as a country artist, it was time for Swift to get a taste of making pure pop music. Red was the first toe-dip into a sound that would come to define much of her career: a seamless blend between her country roots and her pop ambitions. With Martin and his collaborator Shellback, Swift blended guitar riffs with EDM drum fills and dub drops. Gleeful kiss-off “We Are Never Ever Getting Back Together” bait-and-switches with a country guitar riff bleeding into four-on-the-floor bass drum beats and synthesizers. The song would cause a lot of commotion before garnering Swift her first-ever No. 1 hit. On “I Knew You Were Trouble,” Swift is even more experimental, with a full dubstep build-up and drop hitting during the chorus. Swift would save a full-blown pop album for her next; Red was just a bit of a teaser that still focuses on the country sound she was known for. In order to bridge the disparate energies of a synth-explosion like “22” with the down-home twanginess of one like “Stay Stay Stay,” she often finds herself pulling inspiration from the ’80s stadium rock of stars like Bruce Springsteen, U2, and Tom Petty. She goes full “American Girl” on “State of Grace” and makes pal Ed Sheeran the Don Henley to her Stevie Nicks on “Everything Has Changed.” The crown jewel of the album, however, sits at that infamous Track 5 spot. “All Too Well” takes the best of all Swift’s worlds and pours them into an emotional, heart-wrenching, brilliant power ballad. Even Swift herself has regarded it as one of her best, the truest breakup song in an album that she has referred to as her “only true break-up album.”